The present invention relates to an image forming apparatus for conducting image forming by the use of toner in an electrophotographic method, and in particular, to an image forming apparatus and a color image forming apparatus for conducting image forming by developing with two toner types represented by light colored toner and dark colored toner both in the similar color hue.
In an image forming apparatus employing an electrophotographic method, uniform charging is conducted by a charging means on an image forming body which is then subjected to image-wise exposure so that a latent image is formed. The latent image section is then subjected to reversal development by the succeeding developing means, and a toner image is formed. In an image forming apparatus of a digital mode, image-wise exposure is made by dots modulated in terms of a pulse width, for example, and there is conducted reversal development wherein toner is stuck to a section of dots. An amount of toner adhering to the section of dots is determined depending on an area of a dot section on an image forming body, a state of potential, a developing bias for the state of potential and a state of electric charges on toner.
With regard to a section of a high density image recorded by an image exposure means on an image forming body, the number of dots per a unit of area is large, a size of one dot is great, and electric potential falls greatly. On the other hand, With regard to a section of a high density image recorded by an image exposure means on an image forming body, the number of dots per unit area is large, a size of one dot is great, and electric potential falls greatly. With regard to a section of a low density image, on the other hand, the number of dots per unit area is small, a size of one dot is small, and electric potential falls less. Owing to the foregoing, a toner adhesion amount on the section of a high density image on the image forming body after development is large and a toner adhesion amount on the section of a low density image is small. A difference between high image density and low image density on a recorded image is represented by whether the amount of tone per unit area adhering to the image forming body after development is large or small.
However, it is difficult for toner of a single type to form images with excellent gradation. On the highlight section (low density part), in particular, adhesion of toner in extremely small amount per unit area is unstable because of a small size of a dot, thus, image unevenness tends to be caused easily and it is difficult to obtain stable gradation. On the high density part, toner is in the excessive toner adhesion, and image density tends to be saturated, and gradation in a broad area is not obtained. Even if dark colored toner and light colored toner are simply used, a medium density part turns out to be discontinuous or unstable.
The invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (m), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus. Further, the invention is represented by an image forming apparatus wherein reversal development by dark colored toner and reversal development by light colored toner are conducted for one image-wise exposure so that smooth gradation may be obtained without a formation of deviation between a light colored toner image and a dark colored toner image, and thereby image forming is carried out by using dark colored toner and light colored toner.
(1) In the apparatus stated above, the first object of the invention is to provide a monochromatic image forming apparatus employing dark colored toner and light colored toner, wherein there is stipulated characteristic relationship between dark colored toner and light colored toner which can maintain gradation and can obtain stably excellent images.
(2) In the apparatus stated above, the second object of the invention is to provide a color image forming apparatus employing dark colored toner and light colored toner for 4 colors of Y, M, C and K, wherein there is stipulated characteristic relationship between dark colored toner and light colored toner which holds color reproducibility, maintains gradation and can obtain stably excellent color images.
(3) In the apparatus stated above, the third object of the invention is to provide a color image forming apparatus employs transparent toner and white toner in addition to dark colored toner and light colored toner for 4 colors of Y, M, C and K and is capable of obtaining images with higher image quality, wherein there is stipulated characteristic relationship for light colored toner, transparent toner and white toner which makes it possible to obtain excellent color images.
Further, the invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (M), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus. Further, the invention is represented by an image forming apparatus wherein reversal development by dark colored toner and reversal development by light colored toner are conducted for one image-wise exposure so that smooth gradation may be obtained without a formation of deviation between a light colored toner image and a dark colored toner image, and thereby image forming is carried out by using dark colored toner and light colored toner.
(4) In the apparatus stated above, the fourth object of the invention is to provide an image forming apparatus wherein stability of gradation on a highlight portion and improvement of gradation on a high density part are attained by combining processing of image density data and usage of image data for light colored toner and dark colored toner.
(5) In the apparatus stated above, the fifth object of the invention is to provide an image forming apparatus wherein there is provided the most desirable relationship in terms of recorded density between light colored toner and dark colored toner that heightens the effect when forming images with excellent gradation by using light colored toner and dark colored toner.
(6) When forming color images by using light colored toner and dark colored toner, it is necessary to provide developing means respectively for 4 colors of Y, M, C and K each housing therein light colored toner and dark colored toner, resulting in 8 sets of developing units provided to face an image forming body. There may be an image forming apparatus wherein 8 sets of developing units are provided to face an image forming body, and toner images respectively for 4 colors and respectively for light colored toner and dark colored toner are superimposed on an image forming body for image forming, or an image forming apparatus wherein 8 sets of developing units are provided to face respectively 8 image forming bodies, and one toner image for one color for light colored toner and dark colored toner is formed on each image forming body to be superimposed on a transfer sheet. In the apparatus stated above, the sixth object of the invention is to provide an image forming apparatus wherein the size is smaller than that of the aforesaid image forming apparatus and colors can be superposed easily.
(7) In the apparatus stated above, the seventh object of the invention is to provide an image forming apparatus wherein a reproduction area is broadened by using light colored toner and dark colored toner, and further, image quality is improved by reducing splash of dark colored toner on a highlight section which easily stands out conspicuous.
Further, the invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (M), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus.
(8) In the apparatus stated above, the eighth object of the invention is to provide a small-sized image forming apparatus wherein light colored toner and dark colored toner are used depending on images, by combining processing of image density data and usage of image data for light colored toner and dark colored toner, and an image forming apparatus wherein images can be changed depending on purposes for a glossy image, a non-glossy image and an image of OHP.
(9) In the apparatus stated above, the ninth object of the invention is to provide an image forming apparatus wherein continuity of image quality from a low density part to a high density part and continuity of flatness are maintained and excellent properties for transfer can be obtained, by combining processing of image density data and usage of image data for light colored toner and dark colored toner.
(10) In the apparatus stated above, the tenth object of the invention is to provide an image forming apparatus wherein suitable for a color printing apparatus which employs light colored toner and dark colored toner and is especially small in size, and an image forming apparatus that is suitable for selection of how to use light colored toner and dark colored toner depending on images, namely, for example, suitable for selected usage of dark colored toner only for a business documentation.
(11) The eleventh object of the invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (M), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus. In the apparatus stated above, the eleventh object of the invention is to provide an image forming apparatus wherein there is formed an image in which both high resolving power and high gradation can be obtained.
The first object of the invention is attained by either one of the following Structures (1)-(3).
(1) An image forming apparatus that forms a toner image by conducting development of a latent image formed on an image forming body through charging and image-wise exposure by using dark colored toner and development of the latent image by using light colored toner, wherein a difference of an average amount of electrostatic charges between dark colored toner and light colored toner is within 25%.
(2) An image forming apparatus that forms a toner image by conducting development of a latent image formed on an image forming body through charging and image-wise exposure by using dark colored toner and development of the latent image by using light colored toner, wherein a difference of a toner particle size in terms of weight average particle size between dark colored toner and light colored toner is within 25%.
(3) An image forming apparatus that forms a toner image by conducting development of a latent image formed on an image forming body through charging and image-wise exposure by using dark colored toner and development of the latent image by using light colored toner, wherein a difference of an amount of toner adhering to a latent image section in the same potential contrast between dark colored toner and light colored toner is within 25%.
The second object of the invention is attained by either one of the following Structures (4)-(6).
(4) A color image forming apparatus that superposes and transfers, onto a transfer material, a plurality of toner images each being formed on each of plural image forming bodies by conducting development with dark colored toner and development with light colored toner, wherein a difference of an average amount of electrostatic charges among plural color toners is within 25% in all cases.
(5) A color image forming apparatus that superposes and transfers, onto a transfer material, a plurality of toner images each being formed on each of plural image forming bodies by conducting development with dark colored toner and development with light colored toner, wherein a difference of a toner particle size in terms of weight average particle size among plural color toners is within 25% in all cases.
(6) A color image forming apparatus that superposes and transfers, onto a transfer material, a plurality of toner images each being formed on each of plural image forming bodies by conducting development with dark colored toner and development with light colored toner, wherein a difference of an average amount of electrostatic charges among plural color toners is within 25%, and a difference of a toner particle size in terms of weight average particle size among plural color toners is within 25% in all cases.
The third object of the invention is attained by either one of the following Structures (7)-(9).
(7) A color image forming apparatus that conducts development with transparent toner and development with white toner by conducting development with dark colored toner and development with light colored toner for each color for each of plural image forming bodies and thereby superposes the formed toner image on a transfer material for forming, wherein a difference of an average amount of electrostatic charges among each color toner, transparent toner and white toner is within 25% in all cases.
(8) A color image forming apparatus that conducts development with transparent toner and development with white toner by conducting development with dark colored toner and development with light colored toner for each color for each of plural image forming bodies and thereby superposes the formed toner image on a transfer material for forming, wherein a difference of a particle size in terms of weight average particle size among each color toner, transparent toner and white toner is within 25% in all cases.
(9) A color image forming apparatus that conducts development with transparent toner and development with white toner by conducting development with dark colored toner and development with light colored toner for each color for each of plural image forming bodies and thereby superposes the formed toner image on a transfer material for forming, wherein a difference of an average amount of electrostatic charges among each color toner, transparent toner and white toner is within 25% in all cases.
The fourth object of the invention is attained by following Structure (10).
(10) An image forming apparatus that conducts development with light colored toner and development with dark colored toner, based on image data, wherein image data for light colored toner and that for dark colored toner are generated from image density data, and each image-wise exposure is conducted after gradation correction is conducted for each image data.
The fifth object of the invention is attained by following Structure (11).
(11) An image forming apparatus that conducts development with light colored toner and development with dark colored toner, based on image data, wherein a gradient ratio of recording density for light colored toner and dark colored toner is within a range of 0.2-0.5.
The sixth object of the invention is attained by following Structure (12).
(12) An image forming apparatus that conducts development with light colored toner and development with dark colored toner, based on image data, wherein a light colored toner image and a dark colored toner image are superposed on an image forming body through repetition of charging, image-wise exposure and development.
The seventh object of the invention is attained by either one of following Structures (13) and (14).
(13) An image forming apparatus that forms toner images on an image forming body by using light colored toner and dark colored toner, then, transfers and superposes the images on a transfer body, and transfers collectively on a transfer material, wherein a light colored toner image is formed before a dark colored toner image is formed.
(14) An image forming apparatus that forms toner images on an image forming body by using light colored toner and dark colored toner, and transfers and superposes the images on a transfer material, wherein a light colored toner image is formed before a dark colored toner image is formed.
The eighth object of the invention is attained by either one of following Structures (15) and (16).
(15) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner, based on image data, wherein a means for dividing image density data into image data for light colored toner and that for dark colored toner makes image data change that changes a rate of usage for light colored toner and dark colored toner.
(16) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner, based on image data, wherein an image data change that changes glossiness of outputted image is made by a means that divides image density data into image data for light colored toner and that for dark colored toner by using light colored toner whose glossiness is higher than that of dark colored toner.
The ninth object of the invention is attained by either one of following Structures (17), (18) and (19).
(17) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner, based on image data, wherein a means for dividing image density data into image data for light colored toner and that for dark colored toner has image data for light colored toner at a high density part.
(18) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner based on image data and transferring the light colored toner and the dark colored toner onto a transfer material, wherein a layer of light colored toner is positioned to be over a layer of dark colored toner on a transfer material.
(19) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner based on image data and transferring the light colored toner and the dark colored toner onto a transfer material, wherein glossiness of light colored toner is made to be higher than that of dark colored toner, and image data for light colored toner are provided even on a high density part.
The tenth object of the invention is attained by either one of following Structures (20) and (21).
(20) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner, based on image data, wherein a light colored toner image and a dark colored toner image are superposed for image forming on an image forming body through repetition of charging, image-wise exposure and development on an image forming body.
(21) An image forming apparatus conducting image-wise exposure and development with light colored toner and image-wise exposure and development with dark colored toner, based on image data, wherein a light colored toner image and a dark colored toner image are formed on each of two image forming bodies through charging, image-wise exposure and development, and a light colored toner image and a dark colored toner image are superposed.
The eleventh object of the invention is attained by following Structures (22).
(22) An image forming apparatus that is equipped with developing units employing respectively dark and light colored toners in the similar color provided around an image forming body, and conducts development for superposing a dark colored toner image and a light colored toner image, so that the superposed dark colored toner image and light colored toner image are transferred onto a transfer material, wherein an image forming cycle for dark colored toner is made smaller than that for light colored toner.
Incidentally, the image forming cycle stated above is a cycle formed by a dither processing or a pulse width modulation processing.